1. Field of the invention
The present invention relates, in general, to image forming apparatus. In particular, the invention relates to a thermal ink-jet type image forming apparatus wherein a thermal head having a plurality of heating elements and an image formation sheet having a large number of ink permeable holes are employed.
2. Description of the prior art
In recent years, non-impact recording systems such as electrostatic recording systems, thermal-sensitive recording systems, thermal transfer recording systems and ink-jet recording systems have been developed. Of the above recording systems, the ink-jet recording system has advantages in that it operates with a low power consumption and low noise. The ink-jet recording system also has advantages in applications requiring increased miniaturization and in multi-color recording apparatus.
Conventional ink-jet recording systems are shown in FIGS. 1 and 2.
FIG. 1 shows one of the ink-jet recording systems. A diaphragm 31 is vibrated in response to the vibration of a piezoelectric element 33 when an AC voltage is applied to piezoelectric element 33. In response to the vibration of diaphragm 31, ink droplets 34 are ejected from nozzle 35 of the apparatus onto a sheet 37.
FIG. 2 shows another ink-jet recording system. A piezoelectric element 39 is wound around a glass tube 41. When piezoelectric element 39 energized, glass tube 41 is compressed repeatedly in response to the vibration of piezoelectric element 39, and ink droplets are ejected from the nozzle of glass tube 41.
However, in those systems described above, the nozzles of the apparatus often become clogged with ink, and a high density arrangement of the nozzles is extremely difficult.
To solve the above-described problems, a thermal ink-jet system has been developed by applicant's assignee. This thermal ink-jet system includes an image formation sheet having a large number of ink-permeable holes, and a thermal head having a plurality of heating elements. When the heating elements are selectively energized, ink droplets, corresponding to the holes opposite the energized heating elements, are ejected, thus printing an image on a recording sheet.
However, in this type of the thermal ink-jet system described above, the ink between the image formation sheet and the thermal head often dries up when the apparatus is left for an extended period of time after the recording operation is completed. The image formation sheet then adheres to the thermal head with the dried ink. Therefore, the image formation sheet is often ripped or damaged when the image formation sheet is redriven under such condition.